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Introduce 64-bit hash functions with a 64-bit seed.

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This will be useful for hash partitioning, which needs a way to seed
the hash functions to avoid problems such as a hash index on a hash
partitioned table clumping all values into a small portion of the
bucket space; it's also useful for anything that wants a 64-bit hash
value rather than a 32-bit hash value.

Just in case somebody wants a 64-bit hash value that is compatible
with the existing 32-bit hash values, make the low 32-bits of the
64-bit hash value match the 32-bit hash value when the seed is 0.

Robert Haas and Amul Sul

Discussion: http://postgr.es/m/CA+Tgmoafx2yoJuhCQQOL5CocEi-w_uG4S2xT0EtgiJnPGcHW3g@mail.gmail.com
This commit is contained in:
Robert Haas
2017-08-31 22:21:21 -04:00
parent 2d44c58c79
commit 81c5e46c49
33 changed files with 1555 additions and 42 deletions
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43
src/backend/utils/adt/jsonb_util.c
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@ -1249,6 +1249,49 @@ JsonbHashScalarValue(const JsonbValue *scalarVal, uint32 *hash)
*hash ^= tmp;
}
/*
* Hash a value to a 64-bit value, with a seed. Otherwise, similar to
* JsonbHashScalarValue.
*/
void
JsonbHashScalarValueExtended(const JsonbValue *scalarVal, uint64 *hash,
uint64 seed)
{
uint64 tmp;
switch (scalarVal->type)
{
case jbvNull:
tmp = seed + 0x01;
break;
case jbvString:
tmp = DatumGetUInt64(hash_any_extended((const unsigned char *) scalarVal->val.string.val,
scalarVal->val.string.len,
seed));
break;
case jbvNumeric:
tmp = DatumGetUInt64(DirectFunctionCall2(hash_numeric_extended,
NumericGetDatum(scalarVal->val.numeric),
UInt64GetDatum(seed)));
break;
case jbvBool:
if (seed)
tmp = DatumGetUInt64(DirectFunctionCall2(hashcharextended,
BoolGetDatum(scalarVal->val.boolean),
UInt64GetDatum(seed)));
else
tmp = scalarVal->val.boolean ? 0x02 : 0x04;
break;
default:
elog(ERROR, "invalid jsonb scalar type");
break;
}
*hash = ROTATE_HIGH_AND_LOW_32BITS(*hash);
*hash ^= tmp;
}
/*
* Are two scalar JsonbValues of the same type a and b equal?
*/